Manually Painted Vertex Weights don't export to FBX, but auto-weights do
This was due to conflicting vertex groups in the ARP exporter. To fix it, I removed vertex groups that didn't match the secondary controller mode for ARP (which were added in a different bind session set to &quot;none&quot;). In my case, I needed to remove the following groups because my current bind is set to &quot;twist:&quot;
-arm_stretch
-forearm_stretch
-arm_twist
-forearm_twist
-thigh_stretch
-thigh_twist
-leg_stretch
-leg_twist